Balanced housing construction for flexible line trimmer head

ABSTRACT

A housing having a rotary axis and configured to support at least one radially projecting cutting component that effects cutting as the housing is turned around the rotary axis. The housing has a first housing part with a first wall and a plurality of discrete circumferentially spaced cavities in the first wall and each having a volume. The volumes of at least a first and second of the cavities respectively at first and second locations are different and strategically selected to cause a mass distribution on the housing that contributes to improved dynamic balancing of the housing as the housing is turned around the rotary axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/441,921, filed Feb. 24, 2017.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to flexible line trimmers and, more particularly,to a flexible line trimmer having a rotary housing and from which adiscrete length of the line projects to effect cutting as the housingturns.

Background Art

A multitude of trimmers incorporate a rotatable housing from which oneor more cutting components project. As the head is driven around itsaxis, the cutting components effect severance of vegetation, and thelike.

The cutting components may take a variety of different forms. In onecommon construction, a supply of flexible line is wrapped around a coreand has one or more ends that project radially from the housing.

Other designs utilize individual strands or other components that can bemounted to effect cutting in substantially the same manner.

With the exemplary wrapped cutting line arrangement, the supportinghousing is normally made with separable parts. As one example, housinghalves may be used to capture a spool. By separating the housing halves,the spool can be initially installed and thereafter accessed so that itmight be replaced or a line supply may be replenished thereon.

An exemplary form of this construction is shown in U.S. Pat. No.6,952,877, to Pfaltzgraff. In the depicted form, the housing halves aresnap fit using cooperating latch components at diametrically oppositelocations. With the housing halves joined, a user can manually deformcertain of the latch components in a manner that allows the housinghalves to be drawn axially away from each other.

For the convenience of the user, the housings have been constructed witha symmetrical configuration so that the user can align the latchcomponents with the housing parts in two different relationships.

This type of trimmer head is generally common to all categories of thesetools, be they for homeowners or landscape professionals. Since therequirement to replenish line results in down time, those using linetrimmers professionally prefer to have a greater line storage capacity.Such larger capacity line storage heads have been commercially availablefor many years.

Inherent in the larger housing designs is the problem of maintaining adynamic balance. Larger masses with a greater radial extent exaggeratethe effects of manufacturing tolerances that in a smaller design wouldbe potentially limited or even negligible. This problem is compounded bythe speeds at which current trimmer heads are operated to allow forefficient cutting.

Heretofore, the balance problem has been addressed by focusing oncontrolling tolerances in the design and manufacturing processes for thehousing parts. These efforts have generally reduced but not eliminatedimbalances which reflect as vibrations detectable by a user duringoperation. In an extreme case, these vibrations can progressivelyincrease over the lifetime of a product and could potentially lead topart failure.

The above problems are aggravated by the use of lightweight, non-metalmaterials to produce the housing parts through conventional moldingequipment and techniques.

First of all, it is always difficult to maintain close tolerances with amolded part made using a plastic or composite. This problem isaggravated by the fact that the joined parts, with a conventionalconstruction, are prone to skewing during normal operation, as when theyare impacted and/or operated under heavy load and at high speeds. Thisskewing may produce part deformations that affect balance. Joined,non-metal parts also tend to abrade and weld as equipment is utilized,which conditions produce further dynamic imbalance.

Still further, from the point of initial manufacture, it may be verydifficult to engineer tooling to produce well-balanced, fixedconfiguration parts and that maintains the same targeted balancecharacteristics for generated parts as the tooling is used extensivelyand subject to normal wear and reconfiguration.

Further, well-engineered tooling may still produce parts that are lessthan ideally balanced. Once investment in tooling is made for a fixedpart configuration, modifications thereto are impractical and at bestexpensive.

The balance problem is still further aggravated by the ability of a userto assemble housing parts in different manners. Engineers may initiallydesign parts and tooling therefor so that optimal balance results,regardless of how the housing parts are connected. However, on apractical level, variations occur that are uncontrollable and may beattributable to manufacturing methods, manufacturing environments,and/or unusual properties of a particular material molded using thefixed tooling. Thus, housings with parts assembled in different manners,as permitted by their design, may not have the same mass distribution.

These problems become even more pronounced as the size of the trimmerheads increases to provide greater capacity for a stored supply ofcutting line. In spite of this issue, the industry has continued to usethe same basic designs and manufacturing equipment and techniques toproduce trimmer head components. Improvements in this area couldsignificantly distinguish products in a highly competitive marketplace.

SUMMARY OF THE INVENTION

In one form, the invention is directed to a housing having a rotary axisand configured to support at least one radially projecting cuttingcomponent that effects cutting as the housing is turned around therotary axis. The housing has a first housing part with a first wall anda plurality of discrete circumferentially spaced cavities in the firstwall and each having a volume. The volume of at least a first and secondof the cavities respectively at first and second locations is differentand strategically selected to cause a mass distribution on the housingthat contributes to improved dynamic balancing of the housing as thehousing is turned around the rotary axis.

In one form, the first and second cavities have a permanently fixedshape.

In one form, at least a part of the first wall has a moldedconstruction. The first and second cavities are formed in the moldedpart of the first wall.

In one form, the plurality of cavities is made up of at least eightcavities spaced circumferentially around the first housing part.

In one form, the first housing part has an outer circumference. Thefirst and second cavities are each adjacent the outer circumference ofthe first housing part and are circumferentially spaced from each other.

In one form, the first and second cavities each has a cylindrical shapewith an axis substantially parallel to the rotary axis.

In one form, the first and second cavities have a diameter less than ½inch.

In one form, the first and second cavities have a diameter less than ¼inch.

In one form, each of the cavities has a depth. The depth of each cavityextends parallel to the rotary axis. The depths of the first and secondcavities are different.

In one form, the housing has a second housing part with a second wall.The second wall has a plurality of discrete circumferentially spacedcavities each having a volume. The volumes of the plurality of thecavities on the second housing part are strategically selected to causea mass distribution on the housing that contributes to improved dynamicbalancing of the housing as the housing is turned around the rotaryaxis.

In one form, at least a part of the second wall has a moldedconstruction. The plurality of the cavities on the second wall areformed in the molded part of the second wall.

In one form, the second housing part has an outer circumference. Theplurality of cavities in the second wall are each adjacent the outercircumference of the second housing part.

In one form, there are at least eight of the cavities formed in thesecond wall.

In one form, at least one of the cavities in the second wall has avolume different than another of the cavities in the second wall.

In one form, the first and second housing parts cooperatively define aline storage space.

In one form, each of the first and second housing parts has a cup-shapedconfiguration.

In one form, the invention is provided in combination with a spoolhaving a core around which a supply of flexible cutting line is wrapped.The spool is captively maintained between the first and second housingparts with the first and second housing parts connected to each other.

In one form, the first and second housing parts are configured to bereleasably snap-connected to each other.

In one form, the first and second cavities have a same cross-sectionalsize and shape as viewed along the rotary axis.

In one form, a housing has a rotary axis and is configured to support atleast one radially projecting cutting component that effects cutting asthe housing is turned around the rotary axis. The housing includes: afirst housing part with a first wall and a plurality of discretecircumferentially spaced cavities in the first wall and each having avolume, the volume of the cavities strategically selected to cause amass distribution on the housing that contributes to improved dynamicbalancing of the housing as the housing is turned around the rotaryaxis; and a second housing part with a second wall and a plurality ofdiscrete circumferentially spaced cavities in the second wall and eachhaving a volume, the volume of the cavities in the second wallstrategically selected to cause a mass distribution on the housing thatcontributes to improved dynamic balancing of the housing as the housingis turned around the rotary axis.

In one form, the housing has an outer circumference. There are at leastfour of the cavities on each of the first and second walls. The fourcavities on each of the first and second walls are circumferentiallyspaced from the other cavities on respective first and second walls andadjacent to the outer circumference of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a flexible line trimmerincorporating a trimmer head, according to the present invention;

FIG. 2 is a schematic representation of connecting structure between adrive and the trimmer head in FIG. 1;

FIG. 3 is a schematic representation of a structure for manuallyextending line from a spool on the inventive trimmer head in FIG. 1;

FIG. 4 is a schematic representation of a structure for automaticallyextending line from the spool;

FIG. 5 is an exploded, perspective view of one exemplary form of theinventive trimmer head, as shown in schematic form in FIG. 1;

FIG. 6 is an enlarged, bottom, perspective view of the trimmer head inFIG. 5 in an assembled state;

FIG. 7 is a cross-sectional view of the trimmer head taken along line7-7 of FIG. 6;

FIG. 8 is a fragmentary, cross-sectional view showing cooperationbetween components, as shown schematically in FIG. 4;

FIG. 9 is a fragmentary, cross-sectional view of one form of connector,shown schematically on one housing part in FIG. 1, taken along line 9-9of FIG. 5, and a cooperating connector on the other housing part withthe housing parts in an engaged state;

FIGS. 10 and 11 are schematic representations, corresponding to the viewin FIG. 9, and showing the transition of the connectors in FIG. 9 intoan engaged position;

FIG. 12 is a reduced, schematic, plan view of the trimmer head in FIGS.5-7;

FIG. 13 is a schematic representation of interacting parts on the firstand second housing parts that allow the housing parts to be joined inonly one angular relationship;

FIG. 14 is a reduced view as in FIG. 6 from a diametrically oppositeperspective;

FIG. 15 is a schematic representation of an apparatus for formingcomponents/parts making up at least part of a housing on a trimmer head,according to the invention, and including at least one forming cavity inwhich the components/parts are formed;

FIG. 16 is a schematic representation showing certain details of theforming unit on the apparatus in FIG. 15;

FIG. 17 is a schematic representation of a measuring system utilized toanalyze balance of housing components/parts;

FIG. 18 is a bottom view of a housing part made using the apparatus inFIG. 15;

FIG. 19 is a top view of a housing part, made using the apparatus inFIG. 15, and configured to be connected to the housing part in FIG. 18;

FIG. 20 is a schematic representation of a trimmer head with housingcomponents that can be made using the apparatus in FIG. 15; and

FIG. 21 is a flow diagram representation of a method of making at leasta part of a trimmer head housing, according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a schematic representation of a flexible line trimmer isshown at 10, including a rotatable trimmer head, according to theinvention, at 12. The head 12 is mounted on a support 14, whichrepresents a multitude of different types of support that currentlyexist. The support 14 might be a wheeled carriage, a frame that is partof a portable unit that can be carried by a user, etc. The support 14incorporates a suitable drive 16 for the trimmer head 12.

The trimmer head 12 consists of a housing 18 made up of a firstpart/component 20 and a second part/component 22. The housing 18 has anoperating axis around which it moves when powered by the drive 16.

The trimmer head 12 further includes a spool 24 with a core 26 aroundwhich a supply of flexible line 28 is wrapped.

The first and second housing parts 20, 22 are configured to be movedaxially relative to each other between: a) a first state wherein thefirst and second housing parts 20, 22 are separated from each other; andb) a second state wherein the first and second housing parts 20, 22 areoperatively connected.

The housing 18 and spool 24 are configured so that the spool 24: a) ismaintained in an operative position on the housing 18 with the first andsecond housing parts 20, 22 in the second state; and b) can be separatedfrom the housing 18 with the first and second housing parts 20, 22 inthe first state.

As shown additionally in FIG. 2, the trimmer head 12 further includes aconnecting assembly 30 configured to be engaged by the drive 16 that isoperated to cause the housing parts 20, 22 in their second state to bedriven, direct or indirectly, around the operating axis.

The first and second housing parts 20, 22 respectively have connectors32, 34 that cooperate in pairs at at least three different locations. Ateach location, the connector pairs 32, 34 are configured to blockmovement of the first and second housing parts 20, 22 axially away fromeach other with the first and second housing parts 20, 22 in theirsecond state.

Each of the locations where the connector pairs 32, 34 interact isspaced: a) radially from the operating axis; and b) in a circumferentialdirection from the other locations.

The schematic showing of the flexible line trimmer 10 in FIGS. 1 and 2is intended to encompass a wide range of different constructions intowhich the present invention can be incorporated. The inventioncontemplates many variations in the basic components depicted as well astheir interactions. The construction described hereinbelow is intendedto be representative in nature only.

To understand the invention, it is not necessary to understand manydetails of the trimmer head construction. An exemplary trimmer head,consistent with the basic design of the exemplary unit describedhereinbelow, is described in Applicant's U.S. Pat. No. 6,952,877, withinventor Pfaltzgraff. The entire disclosure in U.S. Pat. No. 6,952,877is incorporated herein by reference.

It should be noted that the invention can be incorporated into a trimmerhead that requires manual feeding out of flexible line or one that hasone of a potentially wide range of different feeding mechanisms thatextend line out automatically, including those that require impacting ofthe trimmer head upon a hard surface to effect controlled incrementalline feeding as the trimmer head is rotated in operation.

In FIG. 3, a manual flexible line feeding mechanism is shownschematically at 36 in association with a spool 38 upon which a supplyof flexible line 40 is wrapped.

In FIG. 4, a schematic representation of an automatic line feedmechanism, usable as part of the present invention, is shown inschematic form at 42. The mechanism 42 has a spool 44 that interactswith a housing unit 46 made up of first and second housing parts, asdepicted in FIG. 1. Components 48, 50, respectively on the spool 44 andhousing unit 46, cooperate and are configured to allow incrementalturning of the housing unit 46 relative to the spool 44 upon the housingunit 46 and spool 44 being momentarily axially moved relative to eachother as the housing unit 46 is being turned/rotated by the drive 16.

The particular details of line feeding mechanism are not critical to thepresent invention as the invention can be incorporated into anystructure that has either a manual line feed capability, as shownschematically in FIG. 3, or an automatic feed capability, as shownschematically in FIG. 4 and in Pfaltzgraff's U.S. Pat. No. 6,952,877.

Details of one preferred form of the invention, within the schematicshowings in FIGS. 1-4, will now be described with respect to FIGS. 5-12.

The depicted line trimmer head 12 has the aforementioned housing 18 withfirst and second parts 20, 22, respectively. In most designs, the firsthousing part 20 is an “upper” part and the second housing part 22 is a“lower” part. The housing 18 has an operating axis 52.

The flexible line 28 is wrapped around the core 26 on the spool 24. Thespool 24 has a dividing flange 56 which bounds separate, axially spaced,line storage spaces 58, 60, respectively in conjunction with upper andlower flanges 62, 64.

As described above, the first and second housing parts 20, 22 have firstand second states—a first state as shown in FIG. 5, wherein the firstand second housing parts 20, 22 are separated from each other, and asecond state, as shown in FIGS. 6 and 7, wherein the first and secondhousing parts 20, 22 are operatively connected.

As seen in FIG. 7, with the first and second housing parts 20, 22 intheir second state, the operatively positioned spool 24 is captivelymaintained in an operative position. As seen in FIG. 5, with the firstand second housing parts 20, 22 in their first state, the spool 24 canbe separated from the housing 18 or positioned for assembly.

In this embodiment, the head 12 includes a unitary shaft 66 that extendsbetween the first and second housing parts 20, 22 and through an axialbore 67 through the spool 24. The shaft 66 has axially opposite ends 68,70. The shaft 66 has a stepped diameter.

At an axial mid-portion, the shaft 66 is radially enlarged at 72 todefine a polygonally-shaped perimeter surface 74 that nests in amatching receptacle 76 on the spool 24 and against a part of a surface77 of the spool 24 bounding the bore 67 so that the spool 24 and shaft66 are keyed to rotate together around the axis 52.

Axially oppositely facing, annular shoulders 78, 80, respectively on thespool 24 and shaft 66, abut to consistently maintain a predeterminedaxial relationship between the shaft 66 and spool 24 wherein a throughopening/bore 82 in the shaft 66 aligns with the flange 56 to allow asingle length of the line 28 to be directed radially into and throughthe bore 82. The line 28 projecting from one end of the bore 82 iswrapped in one direction around the core 26 within the line storagespace 58. The line 28 projecting from the other end is wrappedoppositely around the core 26 within the line storage space 60.

With the first and second housing parts 20, 22 in their second state, asshown in FIG. 7, the spool 24 is captively maintained in its operativeposition. More specifically, the spool 24 is captively maintainedbetween axially oppositely facing surfaces 84, 86, respectively on thefirst and second housing parts 20, 22.

The upper flange 62 has a plurality of the aforementioned components 48projecting upwardly therefrom. The components 48 are spaced radiallyfrom the axis 52 and circumferentially around the axis 52 at regularintervals. Each component 48 has a ramp surface 88 and a blockingsurface 90, as seen most clearly in FIG. 8.

The components 48 cooperate with the components 50 that extenddownwardly from the housing part surface 84. The components 50 extendradially from the axis 52 with six such components 50 shown in theexemplary form. The components 48, 50 may be the same, or different, innumber. The components 50 reside in the path of the components 48 as thespool 24 is turned relative to the housing 18 around the axis 52.

The shaft 66 and spool 24 are urged axially upwardly by a biasingcomponent in the form of a coil spring 92 that surrounds a reduceddiameter portion 94 of the shaft 66 at its end 70. The reduced diameterportion 94 is guided vertically within a blind receptacle 96 bounded bya boss 97 on the housing part 22. The spring 92 fits within a separate,surrounding, annular receptacle 98 on the housing part 22, bounded bythe first boss 97 and a second concentric boss 99, and is captivebetween a surface 100 on the housing part 22 and a shoulder 102 definedby a cap 104, surrounding the reduced diameter post portion 94 andnested at the juncture between the radially enlarged region at 72 andthe reduced diameter portion 94. Thus, a constant bias force is normallyproduced by the spring 92 urging the shaft 66 and spool 24 axiallyupwardly to the position shown in FIG. 7.

With the spool 24 in this position, the blocking surfaces 90 on thecomponents 48 axially overlap with blocking surfaces 106 on thecomponents 50. The components 48, 50 are shown to be equal in number andarranged to cooperate simultaneously in the same manner. That is, as thespool 24 is turned in one direction, indicated by the arrow 108 in FIG.8, the blocking surfaces 90, 106 abut to cause the first housing part 20to turn therewith. As explained in greater detail below, the housingpart 22 is connected to the housing part 20, to turn as one piecetherewith.

By turning the spool 24 in the direction of the arrow 110 in FIG. 8, theramp surfaces 88 are caused to engage edges 112 on the components 50,which produces a camming action that progressively moves the spool 24and shaft 66 axially downwardly away from the housing part 20 againstthe force of the spring 92 until the components 48, 50 move past eachother, whereupon the compressed spring 92 urges the spool 24 and shaft66 axially upwardly into the FIG. 7 position. The relative turning ofthe spool 24 and housing 18 causes an unwinding of an increment of theline 28 in the line storage spaces 58, 60 so that free end portions 114,116 of the line 28, that project through diametrically opposite housingopenings 118, 120, project further outwardly to increase their cuttinglengths.

The feeding out of the line 28 can be effected manually with the head 12stationary, or through a bumping action with the head 12 turning inoperation. In the former case, a graspable cap 122 is used to turn theunitary shaft 66. The cap 122 has an inverted cup shape to produce anumbrella shape over, and axially overlapping, the housing part 20. In anormal state for the head 12, a downwardly facing surface 124 on the cap122 is spaced slightly above the top surface 126 of the housing part 20.

The cap 122 has a pair of posts 128, 130 which straddle a reduceddiameter portion 132 of the shaft 66 at its end 68 and nest incomplementary receptacles 134, 136 against the shaft 66. A snap fitconnection can be effected as shown for exemplary post 128 in receptacle134 so that the shaft follows turning movement of the cap 122. With thepost 128 fully seated, an axially facing shoulder 138 thereon snapsunder an axially oppositely facing shoulder 140 on the shaft 66. Thepost 130 may be snap fit in similar fashion into its receptacle 136.

By grasping and turning the cap 122 in one direction, the shaft 66 andspool 24 follow by moving in the direction of the arrow 110. The spool24 can be continuously turned, moving axially upwardly and downwardly asthe components 48, 50 repetitively interact and separate.

The head 12 is rotated by the drive 16 through a component 142 thatengages a threaded bore 144 on the shaft 66 to make up theaforementioned connecting assembly 30. The thread direction is such thatas the drive 16 is operated, this threaded connection is tightened. Theaxially upper end region of the shaft 66 defines a connecting part withthreads that remain exposed to facilitate operative engagement of thedrive 16 through the threaded component 142.

As the shaft 66 is driven, the shaft 66 drives the spool 24 which inturns drives the housing 18 through the cooperating components 48, 50.The rotational direction of the spool 24 is as indicated by the arrow108 in FIG. 8, such that the blocking surfaces 90 on the components 48engage and drive the blocking surfaces 106 on the components 50. Theuser can effect incremental line extension by tapping the bottom surface146 of the housing part 22 against a hard surface as the housing 18 isrotating. As this occurs, the shaft 66 and spool 24 together movemomentarily axially downwardly so as to compress the spring 92. Thisdisengages the components 48, 50 until the restoring force in thecompressed spring 92 returns the shaft 66 and spool 24 to their originalupward positions.

The spool 24 is constructed so that it can be inverted to accommodatedifferent drive directions for the trimmer head 12. The flange 64 hasconnectors 48′ that are oppositely arranged but cooperate with thecomponents 50 otherwise in the same fashion that the connectors 48cooperate therewith.

The housing parts 20, 22 are maintained in their second, connected stateby at least three pairs of the cooperating connectors 32, 34 at spacedlocations and configured to produce a snap fit latching arrangement.Each of the locations is spaced: a) radially from the operating axis 52;and b) in a circumferential direction from the other locations. Thefirst and second housing parts 20, 22, in the second state, are blockedby the cooperating connectors 32, 34 from moving axially away from eachother.

Each connector 34 is in the form of a repositionable, cantilevered latcharm 148 with a leading cam surface 150. The arm 148 further has asurface/edge 152 facing in one axial direction. The arm 148 has a camsurface 153 that extends from the cam surface 150 up to the surface/edge152.

Each connector 32 has a surface/edge 154 facing axially oppositely tothe surface/edge 152 with the housing parts 20, 22 in their secondstate, as shown in FIGS. 7 and 9. The connector 32 has a cam surface 158that blends into a separate cam surface 160 that extends up to thesurface/edge 154.

In the depicted embodiment, the connector pairs 32, 34 are provided atfour circumferentially spaced locations L1, L2, L3, L4 on the head 12.Each of the cooperating connector pairs 32, 34 has the same constructionwith the connectors 32, 34 cooperating in the same fashion when in afully engaged relationship to cooperatively maintain the housing parts20, 22 together in their second state.

As shown in FIGS. 10 and 11, with the housing parts 20, 22 initially intheir first state and axially aligned as in FIG. 10, movement of thehousing parts 20, 22 axially towards and against each other causes thecam surface 150 on each connector 34 to engage the cam surface 158 onthe connector 32. As this relative movement continues, the cooperatingcam surfaces 150, 158 cause the arm 148 to progressively bend radiallyinwardly, as indicated by the arrow 162. The bending of the arm 148continues until the cam surface 153 comes into contact with the camsurface 160, as seen in FIG. 11. Continued relative movement, which isguided by the engaged cam surfaces 153, 160, causes the surfaces/edges152, 154 to move towards each other and eventually past each other,whereupon the arm 148 springs radially outwardly to place thesurfaces/edges 152, 154 in confronting/blocking relationship, as shownin FIG. 9.

With the housing parts 20, 22 in their second state, the free end region164 of each arm 148 is exposed at an opening 166 on the housing part 20such that a radially inward force can be applied thereagainst to bendthe arm 148 radially inwardly to thereby move the surfaces/edges 152,154 out of confronting relationship, whereby the housing parts 20, 22can be separated.

With this arrangement, the housing parts 20, 22 can be axially alignedin their first state and pressed together to thereby be snap fit andlatched/held together in their second state. Of course, the cooperatingconnector parts could be reversed, whereby the bendable arms 148 are onthe housing part 20. Alternatively, one or more bendable arms may beprovided on each of the housing parts 20, 22.

In the depicted form, the arms 148 are molded as one piece with a body168 making up the remainder of the housing part 22. Both of the housingparts are preferably molded from a non-metal material such as a plastic,a composite, etc.

In the exemplary form, the connector pairs 32, 34 at the locations L1and L3 are at diametrically opposite positions. Similarly, the connectorpairs 32, 34 at the locations L2 and L4 are at diametrically oppositepositions. The connector pairs 32, 34 at the locations L1 and L3 aresymmetrical on opposite sides of a reference plane RP1, including theoperating axis 52. The connector pairs 32, 34 at the locations L1 and L3are likewise symmetrical about a separate reference plane RP2 includingthe operating axis 52. As depicted, these reference planes RP1, RP2 arenon-orthogonal to each other.

Inserts 170 of like construction are placed within the housing 18 andactually define the openings 118, 120, which are at fifth and sixthdiametrically opposite locations L5, L6.

In the depicted embodiment, the locations L1-L6 are spaced substantiallyuniformly from each other in a circumferential direction.

The housing part 22 has a series of cantilevered, axially projectingtabs 172, 174 that alternate around the circumference of the housingpart 22. The tab 174 has a generally square shape, with the tab 172having a slightly different polygonal shape.

The tabs 172, 174 are translatable into complementarily-shaped notches176, 178, respectively, on the housing part 20. The tabs 172, 174 nestin their respective notches 176, 178 as the housing parts 20, 22 arechanged from their first state into their second state. The tabs 172,174 and cooperating notches 176, 178 are configured to cooperate to keythe first and second housing parts 20, 22 against relative movementaround the operating axis 52 at the circumferentially spaced locationsat which the tabs 172, 174 and notches 176, 178 cooperate. As depicted,the tabs 172, 174 and notches 176, 178 alternate and are spacedapproximately equidistantly around the circumference of the housing part20.

With the housing parts 20, 22 operatively connected and the latch arms148 snap fit into place, an edge 180 on the housing part 20 abuts to afacing edge 182 on the housing part 22. The edges 180, 182 follow thecontours of their respective body parts around the tabs 172, 174 andnotches 176, 178 to engage substantially fully and continuously aroundthe axis 52. The edges 180, 182 preferably engage at least in theregions between where the connectors 32, 34 reside to stabilize thehousing parts 20, 22 against tipping/skewing.

The unitary shaft 66 is preferably made from a metal material. Byextending fully axially between, and connecting to, each of the firstand second housing parts 20, 22, the shaft stabilizes the housing parts20, 22 to thereby maintain a desired aligned relationship therebetween.By reason of the metal construction of the shaft 66, other cooperatingparts of the housing 12, made from non-metal materials, are not prone towelding to the shaft 66 over time after extended use of the trimmer head12.

The required rigidity for the shaft 66 can be achieved by making theshaft 66 as a single piece or from separate metal pieces that arefixedly connected. For example, the pieces might be welded.

In a preferred form, the shaft 66 is a single, machined piece. Ofcourse, machining of a welded piece is also contemplated. Machiningallows the shaft 66 to be precisely formed with close tolerances.

Weight can be controlled by using a lightweight metal such as aluminum.

Stability is enhanced by having an outer annular surface portion 184 atthe top region of the shaft 66 engaged with a radially inwardly facingannular surface 186 over substantially the entire axial dimension of aboss 188 that locally thickens the upper wall 190 of the housing part20.

The lower region of the shaft 66, the spool 24, and housing part 22interact in a manner to likewise maintain alignment of the housing parts20, 22 and their structural relationship with the spool 24.

The upwardly projecting bosses 97, 99 effectively thicken and rigidifythe housing part 22 and further create enlarged contact areas betweenthe housing part 22 and each of the shaft 66 and spool 24 to therebystabilize the relationship between these components and positively guidetheir relative movement.

More specifically, the boss 97 defines a radially inwardly facingannular surface 191 that cooperates with a radially outwardly facingsurface portion 192 on the reduced diameter portion 94 of the shaft 66.The shaft 66 thus translates axially and turns around the axis 52smoothly relative to the housing part 22 while stably maintaining therelationship of the housing part 22 to the operating axis 52. A radiallyoutwardly facing surface 194 on the boss 97 supports the coil spring 92that extends therearound.

The spool 24 in turn is stably supported for guided movement relative tothe second housing part 22 by the boss 99. The boss 99 has a radiallyoutwardly facing annular surface 196 that bears against a radiallyinwardly facing annular surface 198 on the bottom portion of the spool24. This arrangement stabilizes the spool 24 and smoothly guidesmovement of the spool 24 both axially relative to the second housingpart 22 and as it turns relative to the housing part 22 around the axis52.

The mid to upper region of the spool 24 conforms closely to the shaft 66and is thus stably supported directly by the shaft 66 in that region.

Thus, the housing parts 20, 22 are stably supported by the rigid metalshaft 66, with additional stabilizing of the relationship of the housingparts 20, 22 and shaft 66 afforded by the spool 24 interacting primarilybetween the shaft 66 and housing part 22.

With a precisely formed metal shaft 66 defining the structuralfoundation for the other components on the trimmer head 12, the numberof interacting parts can be reduced. Detrimental stacking of tolerancesmay thus be avoided, as is a resulting imbalanced stack-up. Consistent,balanced alignment of parts may be maintained for the useful lifeexpectancy for the trimmer head 12.

With the above described arrangement, the three or more connectinglocations L1-L4 stabilize the housing parts 20, 22 against tippingrelative to each other, thereby to further maintain overall balance andparts alignment. The latch locations could exceed the four shown.

As noted in the Background Art section herein, another contributor toimbalance is the use of a fixed forming unit/mold construction for thetrimmer head parts/components, particularly the first and second housingparts 20, 22. In spite of steps taken to engineer forming units/molds sothat the housing parts 20, 22 are precisely formed to be dynamicallybalanced, molding of non-metal materials inherently introduces variablesthat may result in shifting of masses on parts, that may be aggravatedas the forming units/molds are repeatedly used and worn and reconfiguredover time.

This imbalance problem is further aggravated by the fact thatconventional housing parts are generally made to be joined together inmore than one relationship. For example, commonly with an arrangement oftwo latch connection locations, for the convenience of a user, thecooperating latch components are configured to cooperate with thehousing parts in each of two different angular relationships. That is,the first and second housing parts can be snap fit together in onerelationship and similarly snap fit together with one of the housingparts turned through 180° relative to the other housing part around therotary axis for the trimmer head.

The inventive housing 18, as described above, may also be constructedwith a symmetrical arrangement which allows the cooperating latchcomponents on the housing parts 20, 22 to be aligned with the housingparts 20, 22 in a least two different angular relationships.

To avoid this latter problem, as shown in FIG. 13, the first housingpart 20 and second housing part 22 may respectively be provided with oneor more interacting parts 200, 202 that that are configured to allow thehousing parts 20, 22 to be joined in only a single angular relationship.

A multitude of different forms of interacting parts 200, 202 may bedevised. The schematic showing of the interacting parts 200, 202 isintended to encompass all such variations, including the interactingparts on the exemplary form of the housing 18 described herein.

More specifically, as seen in FIGS. 5, 6, and 14, the tab 172 on thehousing part 22 performs the function of one of the interacting parts202 shown in FIG. 13, with the complementary edge 204 bounding the notch176 functioning as one of the interacting parts 200. The tab 172 has aperipheral edge 206 matched to the shape of the edge 204 so that the tab172 can be moved axially to be press fit into the notch 176 as thehousing parts 20, 22 are changed from their first state into theirsecond state by being moved axially towards each other with the housingparts 20, 22 maintained in the single angular relationship. The edges204, 206 block any relative angular movement between the housing parts20, 22 in the second state.

At the diametrically opposite location, as shown in FIG. 14, the tab208, functioning as one of the interacting parts 202 on the housing part22, has a truncated, rectangular shape, with a peripheral edge 210 thatseats against a complementarily-shaped edge 212, bounding a notch 214 onthe housing part 20 and functioning as one of the interacting parts 200.The truncated shape, bounded in this embodiment by angled flat edgeportions, produces a tapered leading portion to guide the tab 208 intoits receiving notch 214.

Thus, diametrically opposite pairs of cooperating tabs and notches areprovided. The tabs 172, 208 and notches 176, 214 are symmetrical onopposite sides of a reference plane containing the operating axis 52.

Aside from the tabs 172, 208 having a different shape, as shown, thatmight prevent full axial seating, they also have differentcircumferential widths, CW1, CW2, respectively. Accordingly, the tabwith the larger circumferential width, in this case the tab 172, cannotbe pressed into the notch 214. Thus, the tab 172 blocks movement of thehousing parts 20, 22 into the axial relationship they are in with thehousing parts 20, 22 in the second state.

Thus, the housing parts 20, 22 can be assembled in only one angularrelationship. As a result, in designing the housing parts 20, 22, theycan be precisely dimensioned to produce optimal balance without havingto take into account two alternative relationships of the housing parts20, 22 that may introduce mass shifting that causes a dynamic imbalance.

To further enhance balance, one or both of the housing parts may be madein a manner whereby the mass of a moldable material can be controllablychanged within a fixed cavity, potentially allowing components withdifferent mass distributions to be produced using the same mold cavity.

As shown schematically in FIG. 15, such an apparatus 216 is designed forforming at least a first component making up at least a part of ahousing on a trimmer head. The apparatus 216 will be described as usedto make part or all of the housing parts 20, 22 which, as made using theapparatus 216, will be identified hereinbelow as generally cup-shapedhousing parts 20′, 22′, as seen in FIGS. 18 and 19. However, theapparatus 216 might be used to form part or all of any component on atrimmer head of the type described herein.

The housing part 20′ has a wall 218 that extends continuously around acentral axis 220. The housing part 22′ has a wall 222 extendingcontinuously around a central axis 224, that is substantially coincidentwith the axis 220 with the housing parts 20′, 22′ operatively connected.

While the invention will be described hereinbelow with respect to oneexemplary form, as shown in FIG. 20, the inventive concepts arecontemplated for use with any trimmer head 226 with one or more housingcomponents 228 upon which at least one cutting component 230 issupported that effects cutting as the housing on the trimmer head 226 isturned around a rotary axis. The cutting component(s) may have anynumber of different forms, including a projecting length from a wrappedsupply of flexible line, as described above, or another construction,including but not limited to individual cutting strands or componentsthat project at one or more discrete locations from the housing.

The apparatus 216 consists of a first forming unit/mold 232 defining atleast one cavity 234 within which a moldable material is confined toproduce at least a part of the wall 218 on the housing part 20′ or thewall 222 on the housing part 22′. For purposes of simplicity, theapparatus 216 will be initially described with respect to how it is usedto form the housing part 20′, with it being understood that either orboth of the housing parts 20′, 22′ may be made in substantially the samemanner using the apparatus 216.

The first forming unit 232 is configured to allow selective controllingof a quantity of a moldable material introduced into a first discretesubvolume 236 at a first location in the cavity 234 to thereby allowselective controlling of a mass of a portion of the wall 218 formed bythe moldable material in the cavity 234 at the first location tofacilitate dynamic balancing of a housing made up in part of the housingpart 20′.

The cavity 234 has a shape to confine moldable material to produce theshape of the housing part 20′ in FIG. 18.

As depicted, the first forming unit 232 is configured to allow selectivecontrolling of a quantity of moldable material into a plurality ofdiscrete subvolumes within the cavity 234 with locations correspondingto locations for the subvolume(s) 236 identified as 238 a-238 j on thecompleted housing part 20′.

The housing part 20′ has substantially the same configuration as thehousing part 20, with the primary difference being that at the discretelocations 238 a-238 j there may be different quantities of the moldablematerial, selectively controlled as by an exemplary forming unitstructure shown in FIG. 16.

As depicted, the forming unit 232 has a frame 240 on which the cavity234 is formed. One or more pins 242 is mounted to the frame 240 formovement into and out of the cavity 234. With the pin 242 extended fullyinto the cavity 234, the pin occupies one subvolume within whichmoldable material in the cavity 234 cannot occupy. By strategicallywithdrawing the pin 242, it occupies a smaller subvolume. The openedportion of the one subvolume, resulting from the pin withdrawal, can befilled by the mold material in the cavity 234. Thus, at each location, adiscrete mass of the wall 218 can be controlled to thereby facilitatedynamic balancing of the trimmer head housing into which the housingpart 20′ is incorporated.

Of course, other structures for controlling introduction of moldablematerial into a cavity at discrete locations are contemplated.

While the first forming unit 232 may be configured to allow controllingof a quantity of moldable material introduced into but a single discretesubvolume 236 at a first location, preferably the first forming unit 232is configured to allow selective controlling of a quantity of moldablematerial introduced into at least two discrete subvolumes, as atdiametrically opposite locations.

An exemplary form of the first forming unit 232 is configured to allowselective controlling of moldable material introduced into discretesubvolumes at ten spaced locations to produce the housing part 20′ inFIG. 18. As depicted, the arrangement of the locations 238 issymmetrical about a dividing plane DP including the axis 220 andextending through the centers of the diametrically opposite lineaccommodating inserts 170′.

The locations 238 a-238 j are adjacent to the perimeter/outercircumference 244 of the housing part 20′ to maximize moment arm andbalancing effect. As depicted, the finished housing part 20′ may have upto 10 open cavities C corresponding in number to those locations where apin 242 is not fully withdrawn. While not required, the pins 242 andcavities C may have a cylindrical shape with a varying axial depth andvolume depending upon the position of the pins during the moldingprocess. The diameter of each cavity is preferably less than ½ inch andmore preferably ¼ inch or less. The cylindrical shape is not required,nor is it a requirement that all cavities C have the same shape or size,as depicted. In the embodiment shown, the cavities C have the same sizeand shape as viewed along the rotary axis. The different volumes resultfrom different axial depths.

On each side of the plane DP, the locations 238 are equidistantly spacedfrom each other in a circumferential direction.

It is preferred that there be at least eight such locations/discretesubvolumes 236 in the cavity 234.

As shown in FIG. 15, a second forming unit 248 is provided to producethe housing part 22′, as shown in FIG. 19. The second forming unit 248has the same general construction as the first forming unit 232, with atleast one cavity 250 within which a moldable material is confined toproduce at least a part of the wall 222. The second forming unit 248 isconfigured to allow selective controlling of a quantity of moldablematerial into at least one, and preferably multiple, subvolumes 252 atspaced locations in the cavity 250, which correspond to locations 254a-254 l on the housing part 22′ formed by the second forming unit 248.

The second forming unit 248 may be a separate structure, or part of theapparatus 216, including the first forming unit 232.

As depicted, the housing part 22′ has twelve locations 254 a-254 jspaced around the axis 224 and adjacent to the perimeter/outercircumference 256 of the housing part 22′ at which cavities C1,corresponding to the cavities C, may be formed. Each of the locations254 a-254 l is shown spaced equidistantly from two other locations.While a single location 254 may be provided, preferably multiplelocations, and more preferably at least eight in number, are provided.The locations 254 a-254 l are shown radially spaced from the housingrotary axis the same distance. This is not a requirement.

The cavities C1 may have the same shape and size as the cavities C andmay have different depths and volumes. As shown, the cavities C1 havethe same size and shape as the cavities C as viewed along the rotaryhousing axis, with different axial depths creating different volumes forthe cavities C1.

While the cavities C1 and their locations 238, 254 are shown radiallyspaced the same distance from their respective axis 220, 224, this isnot a requirement.

As shown in FIG. 17, the housing parts 20′, 22′ can be analyzed througha conventional-type measuring system 258. The measuring system 258allows analysis of the mass balance around the rotary operating axis forthe head. The measuring system 258 can be utilized to identify at whichlocations, if any, change in mass distribution is warranted in either ofthe cavities 234, 250 on its respective forming unit 232, 248.

Measuring systems 258 currently exist in the form of machines that candetect angle and force of where an imbalance exists.

Housing parts 20′, 22′ may be analyzed independently or connected toeach other and/or other housing parts/components utilized. The analysismay be carried out both on the individual parts/components and on acompleted trimmer head unit into which the individually analyzedparts/components are incorporated.

A housing can be made using both of the components 20′, 22′ as depicted.Alternatively, either of the housing parts 20′, 22′ might be combinedwith another housing part that does not have the dynamic balancingfeature incorporated.

As shown in flow diagram form in FIG. 21, a method of making at least apart of a trimmer head housing may be carried out as follows.

As shown at block 262, an apparatus as described above is obtained.

As shown at block 264, a moldable material is formed in at least onecavity of a first forming unit with the first forming unit in a firststate, wherein a first discrete subvolume is configured to receiveeither: a) no moldable material; or b) a first quantity of moldablematerial to produce one form of a first component.

As shown at block 266, a dynamic balance state of the one form of thefirst component is measured with respect to its central axis.

As shown at block 268, based upon the measured dynamic balance state ofthe one form of the first component, the first forming unit 232 ischanged from the first state into a second state wherein the firstdiscrete subvolume is configured to receive a different quantity ofmoldable material than received with the first forming unit in the firststate, to thereby produce a second form of the first component.

With the first forming unit in the second state, components/parts can beformed and in turn analyzed, as using a measuring system, as describedabove. Identified imbalances may dictate a further change of the stateof the first forming unit.

As noted above, after forming the one form of the first housingcomponent, the same can be combined with at least one other componentbefore being analyzed using the described measuring system.

The method described above is carried out in the same manner using asecond, different forming unit to produce a second component that hasdifferent forms depending upon the state of the second forming unit. Thestate is changed by controlling the quantity of moldable material thatcan be introduced into subvolumes at various locations within theforming cavity.

The foregoing disclosure of specific embodiments is intended to beillustrative of the broad concepts comprehended by the invention.

1. A housing having a rotary axis and configured to support at least oneradially projecting cutting component that effects cutting as thehousing is turned around the rotary axis, the housing comprising: afirst housing part with a first wall and a plurality of discretecircumferentially spaced cavities in the first wall and each having avolume, the volume of at least a first and second of the cavitiesrespectively at first and second locations being different andstrategically selected to cause a mass distribution on the housing thatcontributes to improved dynamic balancing of the housing as the housingis turned around the rotary axis.
 2. The housing according to claim 1wherein the first and second cavities have a permanently fixed shape. 3.The housing according to claim 2 wherein at least a part of the firstwall has a molded construction and the first and second cavities areformed in the molded part of the first wall.
 4. The housing according toclaim 1 wherein the plurality of cavities comprises at least eightcavities spaced circumferentially around the first housing part.
 5. Thehousing according to claim 1 wherein the first housing part has an outercircumference and the first and second cavities are each adjacent theouter circumference of the first housing part and are circumferentiallyspaced from each other.
 6. The housing according to claim 1 wherein thefirst and second cavities each has a cylindrical shape with an axissubstantially parallel to the rotary axis.
 7. The housing according toclaim 6 wherein the first and second cavities have a diameter less than½ inch.
 8. The housing according to claim 6 wherein the first and secondcavities have a diameter less than ¼ inch.
 9. The housing according toclaim 1 wherein each of the cavities has a depth, the depth of eachcavity extends parallel to the rotary axis, and the depths of the firstand second cavities are different.
 10. The housing according to claim 1wherein the housing comprises a second housing part with a second wall,the second wall having a plurality of discrete circumferentially spacedcavities each having a volume, the volumes of the plurality of thecavities on the second housing part strategically selected to cause amass distribution on the housing that contributes to improved dynamicbalancing of the housing as the housing is turned around the rotaryaxis.
 11. The housing according to claim 10 wherein at least a part ofthe second wall has a molded construction and the plurality of thecavities on the second wall are formed in the molded part of the secondwall.
 12. The housing according to claim 10 wherein the second housingpart has an outer circumference and the plurality of cavities in thesecond wall are each adjacent the outer circumference of the secondhousing part.
 13. The housing according to claim 10 wherein there are atleast eight of the cavities formed in the second wall.
 14. The housingaccording to claim 10 wherein at least one of the cavities in the secondwall has a volume different than another of the cavities in the secondwall.
 15. The housing according to claim 10 wherein the first and secondhousing parts cooperatively define a line storage space.
 16. The housingaccording to claim 15 wherein each of the first and second housing partshas a cup-shaped configuration.
 17. The housing according to claim 16 incombination with a spool having a core around which a supply of flexiblecutting line is wrapped, the spool captively maintained between thefirst and second housing parts with the first and second housing partsconnected to each other.
 18. The housing according to claim 17 whereinthe first and second housing parts are configured to be releasablysnap-connected to each other.
 19. The housing according to claim 1wherein the first and second cavities have a same cross-sectional sizeand shape as viewed along the rotary axis.
 20. A housing having a rotaryaxis and configured to support at least one radially projecting cuttingcomponent that effects cutting as the housing is turned around therotary axis, the housing comprising: a first housing part with a firstwall and a plurality of discrete circumferentially spaced cavities inthe first wall and each having a volume, the volume of the cavitiesstrategically selected to cause a mass distribution on the housing thatcontributes to improved dynamic balancing of the housing as the housingis turned around the rotary axis; and a second housing part with asecond wall and a plurality of discrete circumferentially spacedcavities in the second wall and each having a volume, the volume of thecavities in the second wall strategically selected to cause a massdistribution on the housing that contributes to improved dynamicbalancing of the housing as the housing is turned around the rotaryaxis.
 21. The housing according to claim 20 wherein the housing has anouter circumference and there are at least four of the cavities on eachof the first and second walls, and the four cavities on each of thefirst and second walls are circumferentially spaced from the othercavities on respective first and second walls and adjacent to the outercircumference of the housing.